python ast.literal_eval和datetime

Question

我有一个字符串"{'datetime': datetime.datetime(2010, 11, 21, 0, 56, 58)}"，我想将其转换为它代表的对象。使用ast.literal_eval()给

ValueError: malformed string;

因为它不允许构造对象（即datetime调用）。无论如何，要么可以ast正确地处理此问题，要么可以确保eval防止代码注入？

Answer 1

跟随伊格纳西奥·巴斯克斯（Ignacio Vazquez-brams）的想法：

import ast
import datetime

def parse_datetime_dict(astr,debug=False):
    try: tree=ast.parse(astr)
    except SyntaxError: raise ValueError(astr)
    for node in ast.walk(tree):
        if isinstance(node,(ast.Module,ast.Expr,ast.Dict,ast.Str,
                            ast.Attribute,ast.Num,ast.Name,ast.Load, ast.Tuple)): continue
        if (isinstance(node,ast.Call)
                and isinstance(node.func, ast.Attribute)
                and node.func.attr == 'datetime'): continue
        if debug:
            attrs=[attr for attr in dir(node) if not attr.startswith('__')]
            print(node)
            for attrname in attrs:
                print('    {k} ==> {v}'.format(k=attrname,v=getattr(node,attrname)))
        raise ValueError(astr)
    return eval(astr)

good_strings=["{'the_datetime': datetime.datetime(2010, 11, 21, 0, 56, 58)}"]
bad_strings=["__import__('os'); os.unlink",
             "import os; os.unlink",
             "import(os)", # SyntaxError
             ]

for astr in good_strings:
    result=parse_datetime_dict(astr)    
    print('{s} ... [PASSED]'.format(s=astr))

for astr in bad_strings:
    try:
        result=parse_datetime_dict(astr)
    except ValueError:
        print('{s} ... [REJECTED]'.format(s=astr))
    else:
        sys.exit('ERROR: failed to catch {s!r}'.format(s=astr))

产量

{'the_datetime': datetime.datetime(2010, 11, 21, 0, 56, 58)} ... [PASSED]
__import__('os'); os.unlink ... [REJECTED]
import os; os.unlink ... [REJECTED]
import(os) ... [REJECTED]